The energy transition is underway, so we need to prioritize efforts to make mining more sustainable. As we move towards a mineral-dependent energy system, we will dedicate more of the world’s resources to extracting and refining the precious materials we need for energy storage. As a result, our demand for minerals like copper, nickel, lithium, and cobalt may grow by 500% in the next decade.
In previous articles, we’ve discussed the demand for these materials and their associated costs. Right now, it’s time to think about how to be proactive about mining, to make it as earth-friendly and sustainable as possible. By the way, trying to make mining more sustainable isn’t merely the right thing to do from an environmental standpoint. There are considerable benefits to investors, and our actions today will significantly impact the future of manufacturing.
Let’s start with a high-level overview of the extraction process. For most commodity materials — copper, gold, etc. — the process begins with quarries into the earth’s crust. Large amounts of ore-bearing materials are brought to the surface. From there, the material is processed and refined. Each mineral needed for the energy transition requires a different collection process, but this will help us understand the basics.
The Mining & Refining Process
Here, we’ll explore how minerals get to manufacturers in a usable form. Once we understand the process, we can look for points to make mining more sustainable.
The Quarry
Copper, for example, is usually mined using open-pit mining. The quarry is a series of stepped benches, which are dug deeper and deeper into the earth. Boring machinery is used to drill holes into hard rock, and explosives are inserted into those holes to blast and break the rock. This creates boulders, which are then hauled by trucks or rail cars to a processing site, usually nearby.
The Primary Crusher
Once at the processing site, the boulders go through a primary crusher. The primary crusher reduces boulders to golf ball-sized chunks of material. Organizations use hydrometallurgy or pyrometallurgy to remove copper from the host material.
- As their names imply, hydrometallurgy processes use water, while pyrometallurgy requires extremely high temperatures.
- Hydrometallurgical processes are more common in the copper business right now, but that may change as our needs for freshwater change.
Next, the material undergoes heap leaching.
Heap Leaching
The golf-ball-sized crushed ore is piled into a heap on a slight slope of impenetrable material. Diluted sulfuric acid is sprayed onto the heap and allowed to trickle through the material and down the slope. The “pregnant” leach solution of sulfuric acid and copper sulfate collects in a pool below, and it’s about 60-70% copper at this point.
Now comes solvent extraction.
Solvent Extraction
Two immiscible liquids — non-mixing, like oil in water — are stirred and allowed to separate in the pool. The cooper moves from one liquid to the other. Then, this solution is mixed with a solvent. The copper migrates from the leach solution into the solvent.
The two liquids separate, and the copper remains in the solution in the solvent. Impurities are left in the leach solution. The leftover leach solution can then be recycled by adding additional sulfuric acid. From there, it’s sent back up to the heap to be sprayed on the next load of ore.
Finally, the solution is ready for the last step.
Electrowinning
Electrowinning is a type of electrolysis. An electrical current is passed through the copper solution, which acts as an electrolyte. Then, positively-charged copper ions — known as cations — come out of the solution and are plated onto a cathode. The final result is 99.99% pure copper. It’s ready to be pulled into wire, plated onto tidbits for technology, or mixed with other metals to create the alloys we need for things like currency, statuary, and energy storage.
Now that we can imagine the process from start to finish, let’s poke around at the process and look for ways to improve sustainability.
Addressing Sustainability in Mining
Open-pit mining, like our copper mine described above, is considered the most environmentally hazardous method of ore extraction among recognized organizations. There’s damage to the earth’s crust and tremendous amounts of diesel fuel used, which create greenhouse gas (GHG) emissions. And, after all, the energy transition is about reducing our GHGs.
Perhaps the only more dangerous type of mining is unrecognized, back-alley, non-permitted, illegal mining, and that’s a story for another day.
So, what can we do about the sustainability issues? Let’s explore a few options and start brainstorming for more.
In Situ Leaching
Some organizations are turning to another type of mining, called in situ leaching (ISL) or in situ recovery (ISR.)
Rather than digging a giant pit, transporting ore, and crushing it, ISR processes leave the ore in the ground. They recover minerals by dissolving them with leaching solutions. Then, the pregnant solution is pumped to the surface. From there, it can undergo refining processes like solvent extraction and electrowinning.
The benefits of ISR include:
- Very little surface disturbance; earth-scarring and deforestation are less problematic
- No tailings — waste rock — are generated (we’ll talk more about tailings in a moment)
- Less reliance on diesel fuel, which leads to fewer GHG emissions and perhaps a slight improvement in diesel prices
There are a few caveats, of course. The ore must be permeable so the leaching solutions can get in there and work. And the whole operation needs to be located far from groundwater sources. Otherwise, we risk contaminating the water table with dangerous reagents.
ISR isn’t a new type of mining. We’ve been using this method to harvest uranium for years. But it might be a more environmentally responsible choice as the energy transition carries on.
We can also work harder to reuse mine waste.
On Reusing Mining Waste
Mining and extraction produce tremendous amounts of waste, including tailings and wastewater. Historically, mining organizations have left that waste behind when mining operations cease. Sometimes mining waste is stored in tailings dams, which can fail catastrophically.
But there are several ways we can reuse mine waste. For example, mining organizations can use the waste rock on site. It can be used to backfill voids, refill spent shafts and quarries, and build up the local terrain to prevent erosion.
Mine water can be treated and reused for agriculture or on-site dust control.
Even the toxic tailings left behind in mine sites or stored in large-scale tailings dams could someday find eco-friendly use. Perhaps they can be treated and used for infrastructure materials, construction materials, or insulation. These ideas are relatively new, but that makes them very exciting.
Mine Waste for Decarbonization
New research suggests certain types of tailings — remember, these are semi-toxic leavings and waste rock material — can be treated to make them absorb CO2 like a sponge. Perhaps we can bury some of that sequestered carbon in dead quarries and cap them like landfills.
Alternatively, imagine building structures, bridges, and highways out of that rocky material. Perhaps blocks of CO2 sponges could be coated or treated and used to make sidewalks, skyscrapers, or wind turbines. The environmental benefits could be terrific, and the international market for such a material, once perfected, would be enormous.
Of course, there’s still a lot of research to be done. We need to understand the long-term reactions and ask big questions like “Is there a half-life for carbon capture?” But the organizations that master it and put it to use will see a tremendous return on their investment (ROI.)
Will EVs Work at Mines?
Maybe, someday, it’s possible. As we’ve already mentioned, current mining methods rely on diesel fuel. Remember, those vast boulders must be moved from the pit to the primary crusher. Once crushed, it needs to be transported to the leach heap. From there, the processed material must also be removed. Diesel fuel powers the way at every step.
In the future, electric vehicles might be capable of handling some of that work. As of 2022, while electric trucks are available for consumers, they don’t have tremendous towing capability. We’ll need to develop better energy storage for this solution to work. Otherwise, we’re creating a chicken-and-egg problem, using the EVs to mine the minerals we need for EVs.
Who Should Be Responsible for Making Mining More Sustainable?
Historically, the mining organization simply left when a site was mined out. In their wake were mountains of rubble, toxic groundwater, tailing dams, and a scarred earth. But the game needs to change, and we need the players to lean into new technology and methods with enthusiasm.
Of course, we never hesitate to drop names. The major players in the extraction industry include big names like:
- Glencore PLC
- BHP Group Ltd.
- Rio Tinto
- Jiangxi Copper Co. Ltd.
- And Vale SA
Together, these organizations generate about $300 billion in revenue annually. Hopefully, we can count on them to continue researching and developing cleaner mining techniques and better waste use.
Related Reading & Resources:
Empoweringpumps.com: 5 Ways to Make Mining More Sustainable
Smenet.org: What are Tailings?
Phys.org: Scientists Identify New Minerals for Carbon Capture
Cen.aes.org: The Life-or-Death Race to Improve Carbon Capture
